This invention relates to a guide wire used to introduce a catheter to a necessary position in a human body for a remedy or an examination.
A catheter is used in medical treatment such as super selective angiography, percutaneous transluminal angioplasty (PTA), transcatheter arterial embolization (TAE) or percutaneous transluminal coronary angioplasty (PTCA), etc. In order to introduce the catheter into a human body, a guide wire has been heretofore used. The guide wire is a wire for guiding a catheter. The guide wire is mainly used in a percutaneous catheterization (Seldinger method). In this method, after a guide wire is inserted into a blood vessel, a catheter is inserted into a blood vessel with the guide wire used as a shaft. It is very difficult to insert a catheter into an artery because the pressure in an artery is higher than that in a vein. The catheter can be easily inserted into an artery by placing a guide wire in the artery in advance, and inserting a catheter thereinto along the guide wire.
A guide wire is comprised of, for example, an elongated core wire and a coil wire provided on an outer circumference of a distal end portion of the core wire as disclosed in U.S. Pat. No. 4,846,186, Japanese Patent Laid-Open Nos. 54911/1994 and 54912/1994 and Japanese Utility Model Laid-Open No. 37199/1995. The core wire is a core member, which becomes thin toward the distal end thereof and is formed out of a super-elastic material. The super-elastic material needs to have a suitable flexibility to give follow-up characteristics with respect to a blood vessel, i.e., the capability to select a proper blood vessel at a branch point, to the guide wire and a rigidity high enough to transmit a torque and a pushing force generated at a proximal end of the guide wire to a distal end thereof. The coil wire can be reshaped by plastically deforming the same, and is a metal coil excellent in operability and radiolucency. The core wire and the coil wire are combined by melting a part of the distal end portion of the coil wire to form a guide wire. A guide wire formed by combining the core wire and the coil wire can be deformed at a distal end portion thereof and easily passes through a narrowed portion in a blood vessel. Moreover, the guide wire is formed so that a turning movement generated at a proximal end thereof can be smoothly transmitted to a distal end portion thereof.
A guide wire is occasionally bent or plastically deformed by medical personnel in advance to fit the shape of the guide wire to a shape of a portion of a blood vessel into which a guide wire is to be inserted. In such a case, a guide wire has been developed of which the core wire is provided with an additional attachment called a ribbon at the distal end thereof in order to absolutely and easily deform the distal end of the guide wire (Japanese Patent Laid-Open Nos. 292174/1992, 505561/1995 and 99092/1997 and U.S. Pat. Nos. 4,554,929, 4,998,917 and 5,135,503).
All of the guide wires disclosed in the above-mentioned publications are formed so that the distal end portion thereof is more flexible than the proximal end portion in order to improve a follow-up characteristic with respect to a blood vessel. That is, the core wire composing the guide wire becomes thin toward the distal end thereof, and the ribbon provided at the distal end of the core wire consists of a material having an excellent flexibility or has a smaller cross-sectional area than that of the distal end of the core wire. However, as described above, the core wire needs to provide not only flexibility to the distal end portion of the guide wire but also rigidity high enough to transmit a torque and a pushing force generated at a proximal end of the guide wire to the distal end thereof. Therefore, there is a limit to the extent of reduction of the diameter of the distal end portion of the core wire.
The core wires disclosed in the above-mentioned publications are formed so that the distal end portion of each core wire has a columnar or tabular shape having a constant diameter or width, the rigidity of the distal end portion being thereby maintained. However, since a portion having a constant width in the distal end portion of the core wire has a constant degree of flexibility, i.e. hardness, the rigidity of the distal end portion of the guide wire becomes high. Therefore, there is a fear that the distal end of the guide wire will puncture a blood vessel due to a pushing force transmitted from the proximal end of the guide wire. When a material of the distal end portion of the core wire is changed to a material capable of giving flexibility to the guide wire, it is difficult for torque generated at the proximal end of the guide wire to be transmitted to the distal end thereof.